Download Lesson 10 - Arrowhead Union High School

Lesson 10.5 Modeling with Trigonometric Equations
Objective: Write and solve trigonometric functions that model situatuions.
Example A
Fox Population Problem:
Naturalists find that populations of some kinds of predatory animals vary periodically with
time. Assume that the population of foxes in a certain forest varies sinusoidally with time.
Records started being kept at time t = 0 yr. A minimum number of 200 foxes appeared at t = 2.9
yr. The next maximum, 800 foxes, occurred at t = 5.1 yr.
Find an equation that matches the situation
Foxes are declared an endangered species when their population drops below 300.
Between what two nonnegative values of t were the foxes first endangered?
What is the next interval when the foxes will be endangered?
Homework: Worksheet
Lesson 10-5 Homework
Practice Solving Trigonometric Equations and Modeling Sinusoidal Functions
Solve the following equations on the specified domain. (Round all solutions to the nearest thousandth)
sin   0.438
1.
0    2
2.
cos   0.3
0 o    360 o
3.
7 tan   2
0    2
4.
5 cos   1  0
General solution (radians)
5.
3 cos   7
General solution (degrees)
6.
sin   0.9
7.
tan   2.37
General solution (radians)
8.
5 sin( 2 x  1)  1
General solution (degrees)
0    6
9.
12 cos2t   10
General solution (radians)
10.
10 sin x  3   5  7
0    10
11.
One more Ferris Wheel Problem: The world’s tallest Ferris wheel is the Singapore Flyer which
measures 165 meters tall, and has a diameter of 150 meters. After you get on the Ferris wheel
you reach the highest point after 23 minutes and then reaches its lowest point after 38 minutes.
a.
The height of a person on the Ferris wheel over time forms a sinusoidal curve. Find an
equation for the height of a rider after getting on the wheel.
b.
12.
The time between high and low tide in a river harbor is approximately 7 h. The
high-tide depth of 16 ft occurs at noon and the average harbor depth is 11 ft.
a.
Write an equation modeling this relationship.
b.
13.
Give two intervals of time when the height of the rider is higher than 155 meters.
If a boat requires a harbor depth of at least 9 ft, find the next two time periods
when the boat will not be able to enter the harbor.
Bouncing Spring Problem: A weight attached to the end of a long spring is bouncing up and
down. As it bounces, its distance from the floor varies sinusoidally with time. You start a
stopwatch. When the stopwatch reads 0.3 s, the weight first reaches a high point 60 cm above
the floor. The next low point, 40 cm above the floor, occurs at 1.8 s.
a.
Find a particular equation for distance from the floor as a function of time.
b.
What is the distance from the floor when the stopwatch reads 17.2 s?
c.
What is the first positive value of time when the weight is 59 cm above the floor?